Systems and methods for tracing aircraft vortices

ABSTRACT

Systems and methods for tracing aircraft vortices are disclosed. One method includes directing a tracer from a first aircraft into a vortical flow generated by the first aircraft. The method can further include detecting a characteristic corresponding to the presence of the tracer directed into the vortical flow. Based at least in part on the detected characteristic, the method can include directing the flight of the first aircraft, or a second aircraft following the first aircraft, or both.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. applicationSer. No. 11/463,685, titled “Aircraft Wake Vortex Predictor andVisualizer,” filed on Aug. 10, 2006 and incorporated herein in itsentirety by reference.

TECHNICAL FIELD

Aspects of the present disclosure are directed generally toward systemsand methods for tracing aircraft vortices.

BACKGROUND

Air traffic volumes continue to grow, and the capacity limitations atairports are causing increasing flight delays. The capacity limitationscome, in part, from wake turbulence created by aircraft, which limitshow closely aircraft can be spaced during takeoff and landing. Theselimitations apply to both single runway operations and parallel runwayoperations. Typically, for example, aircraft takeoffs and landings willbe spaced by up to three minutes, depending on how much smaller thefollowing aircraft is than the leading aircraft. This spacing allowsturbulence to move off the runway and flight path, or to dissipate,before the following aircraft encounters the turbulence.

Wake turbulence is generated in the form of vortices trailing fromaircraft wing tips and other lifting surfaces. The pair of vorticesgenerated by each aircraft is the result of lift being generated by thewings and air rotating around the wing tip from the high pressureregions at the bottom of the wing to the low pressure regions at the topof the wing. The strength of the vortices depends upon the aircraftspeed and configuration, and upon the instantaneous lift being generatedby the wing. While there are ways to reduce the strength of thevortices, they cannot be eliminated. The vortices can severely buffetanother aircraft that flies into them, and the vortices from a transportaircraft flying at landing or take-off speeds can upend small aircraftand cause them to lose control.

Wing tip vortices generally cannot be directly visualized at lowaltitudes, except in rare atmospheric conditions. In researchexperiments, wake turbulence has been measured with sophisticated andcostly laser Doppler devices positioned along the flight path. Thelasers are typically aimed across the flight path to detect thecharacteristic approaching and receding motions of air within thevortices. Such equipment, however, does not operate in all weatherconditions and may be too costly for routine airport operations. As aresult, aircraft takeoff and landing separations are typicallyestablished assuming the worst conditions. This may apply not only tosingle runways but also to dual approach paths associated with runwayssignificantly less than one mile apart. These minimum separations areoften greater than what would be adequate for complete safety if thelocation and movement of the vortices were known with certainty so thatthey could be avoided with minor changes in flight path. Accordingly,there is a need for improved methods and systems for detecting andresponding to aircraft vortices.

SUMMARY

The following summary is provided for the benefit of the reader only,and is not intended to limit in any way the scope of the invention asset forth by the claims. Aspects of the present disclosure are directedto systems and methods for tracing aircraft vortices. A method foridentifying aircraft vortical flows in association with one aspectincludes directing a tracer from a first aircraft into a vortical flowgenerated by the first aircraft, and detecting a characteristiccorresponding to the presence of the tracer directed into the vorticalflow. The method can further include, based at least in part on thedetected characteristic, directing the flight of the first aircraft, ora second aircraft following the first aircraft, or both. For example,the method can include controlling a separation distance between thefirst aircraft and the second aircraft, and/or directing the secondaircraft away from the vortical flow.

The tracer can include a gas (e.g., a gas that is lighter than air) sothat the tracer tends to move to the center of the vortex. In otherembodiments, the gas can be contained in envelopes (e.g., smallballoons). In still further embodiments, the tracer can include chaff orother solid objects deployed from the aircraft. In yet furtherembodiments, the tracer can include energy. For example, the tracer caninclude energy that is directed into the air entrained in the vorticalflow so as to ionize air molecules in the vortical flow. The ionized airmolecules are detectable and distinguishable from the surroundingnon-ionized air molecules, e.g., via radar. In other embodiments,directing energy into the vortical flow can include changing othercharacteristics of the air molecules. For example, the directed energycan increase the electronic state of an air molecule, and the energyemitted by the molecule as it returns to its initial energy state canthen be detected. In any of the foregoing embodiments, the tracer can bedirected in a time-varying manner to distinguish the tracer from itsenvironment.

A method for identifying aircraft vortical flows in association withanother aspect includes generating a vortical flow in air adjacent to anaircraft by moving the aircraft relative to the adjacent air, anddirecting a tracer from the aircraft into the vortical flow. The traceris visually indistinguishable from its surroundings to an unaidedobserver on the ground or in a following aircraft while the tracer is inthe vortical flow.

A method in accordance with another aspect includes detecting acharacteristic correlated with the presence of a tracer directed from anaircraft into vortical flow in air adjacent to the aircraft as theaircraft moves relative to the adjacent air. The tracer is visuallyindistinguishable from its surroundings to an unaided observer on theground or in a following aircraft while the tracer is in the vorticalflow. The method can further include generating a signal in response todetecting the presence of the tracer.

In further particular aspects, the method can further includecontrolling a separation distance between a first aircraft (from whichthe tracer is directed) and a second aircraft following the firstaircraft, or directing the second aircraft away from the vortical flow,or both controlling the separation distance and directing the secondaircraft away from the vortical flow, based at least in part on thegenerated signal. The characteristic correlated with the tracer can bedetected from the ground or from another aircraft. In furtherembodiments, energy can be added to the tracer and the method canfurther include detecting energy emitted by the tracer.

Still another aspect is directed to an aircraft that includes a payloadvolume, a lifting surface positioned to generate lift and an associatedvortical flow, and an onboard vortical flow tracer system that includesa tracer director positioned to direct a tracer into vortical flowgenerated by lifting surface, with the tracer being visuallyindistinguishable from its surroundings to an unaided observer on theground or in a following aircraft while the tracer is in the vorticalflow. The vortical flow tracer system can further include a controlleroperatively coupled to the tracer director to selectively activate thetracer director.

Still another aspect is directed to a system for identifying vorticalflow, which includes a ground-based detector having a detection vectoraligned axially with an active runway final approach/departure axis. Acontroller is operatively coupled to the detector, and an output deviceis operatively coupled to the detector to provide an indication when thedetector identifies a characteristic associated with a tracer in avortical flow. In particular embodiments, the detector can include atleast one of a radio signal detector, a radar detector, a lidardetector, or an optical detector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system for directing tracersinto aircraft vortical flows, detecting the tracers, and providing anassociated feedback.

FIG. 2 is a partially schematic illustration of an aircraft havingtracer directors configured in accordance with several embodiments ofthe invention.

FIG. 3 is an enlarged, partially schematic illustration of a wing tipregion housing tracer directors in accordance with several embodimentsof the invention.

FIG. 4 is an enlarged illustration of a portion of an aircraft wing tiphousing a tracer director that directs energy into a vortical flow inaccordance with an embodiment of the invention.

FIG. 5 is a flow diagram illustrating a process for directing tracersfrom an aircraft into a vortical flow generated by the aircraft.

FIG. 6 is a flow diagram illustrating a process for detecting acharacteristic associated with the presence of tracers directed from anaircraft into its vortical flow.

FIG. 7 is a partially schematic top view of an aircraft approaching aground-based tracer detector positioned and configured in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION

The following description is directed generally toward systems andmethods for tracing aircraft vortices. Several details describingstructures or processes that are well-known and often associated withaspects of the systems and methods are not set forth in the followingdescription for purposes of brevity. Moreover, although the followingdisclosure sets forth several embodiments of different aspects of theinvention, several other embodiments of the invention can have differentconfigurations or different components than those described in thissection. As such, the invention may have other embodiments withadditional elements or without several of the elements described belowwith reference to FIGS. 1-7.

Several embodiments of the invention described below may take the formof computer-executable instructions, including routines executed by aprogrammable computer. Those skilled in the relevant art will appreciatethat the invention can be practiced on computer systems other than thoseshown and described below. The invention can be embodied in aspecial-purpose computer or data processor that is specificallyprogrammed, configured or constructed to perform one or more of thecomputer-executable instructions described below. Accordingly, the term“computer” as generally used herein refers to any data processor and caninclude Internet appliances and hand-held devices (including palm-topcomputers, wearable computers, cellular or mobile phones,multi-processor systems, processor-based or programmable consumerelectronics, network computers, mini-computers and the like).Information handled by these computers can be presented at any suitabledisplay medium, including a CRT display or LCD.

The invention can also be practiced in distributed environments, wheretasks or modules are performed by remote processing devices that arelinked through a communication network. In a distributed computingenvironment, program modules or subroutines may be located in local andremote memory storage devices. Aspects of the invention described belowmay be stored or distributed on computer-readable media, includingmagnetic or optical readable or removable computer disks, as well asdistributed electronically over networks. Data structures andtransmissions of data particular to aspects of the invention are alsoencompassed within the scope of the invention.

FIG. 1 is a schematic illustration of a system 100 for directing tracersinto aircraft vortical flows, and detecting characteristics associatedwith the presence of the tracers in the vortical flows. This system 100generally include a tracer director 120 carried by an aircraft, and atracer detector 130, portions of which may be carried by one or moreaircraft, and other portions of which may be ground-based. Aspects ofthe overall system are described below with reference to FIG. 1. Aspectsof particular embodiments of the tracer directors 120 are then describedwith reference to FIGS. 2-4. The operation of the tracer directors anddetectors are described with reference to flow diagrams shown in FIGS. 5and 6, respectively, and FIG. 7 illustrates a tracer detector configuredin accordance with a particular embodiment of the invention.

By operating the tracer director and tracer detector in accordance withparticular embodiments of the invention, operators can more accuratelyidentify the location of aircraft vortices and can direct followingaircraft (and/or other aircraft) in accordance with this information. Asa result, aircraft controllers can space aircraft according to actualvortex data, which is expected to reduce aircraft following distanceswhen compared with traditional techniques that often assume vortexconditions more severe than they actually are.

The tracer directors 120 can be carried by one or more aircraft 110,shown in FIG. 1 as a first or leading aircraft 110 a and a second orfollowing aircraft 110 b. The tracer directors 120 direct a tracer intothe aircraft wake vortices 111 generated by the aircraft 110 a, 110 b,where characteristics associated with the tracers can be detected by thetracer detector 130. Optionally, the characteristics can be made moredetectable to the tracer detector 130 by energy directed into thevortices from an aircraft-based source or a ground-based source 135. Theinformation obtained by the tracer detector 130 corresponds to thelocation of the vortices 111. The tracer detector 130 can include one ormore detector elements, for example, a ground-based detector 131 and/orone or more airborne detectors. The airborne detectors can include afirst airborne detector 132 positioned to detect the presence of thevortex 111 generated by the aircraft in which it is housed. Accordingly,the first airborne detector 132 on the leading aircraft 110 a can bepositioned to detect the vortex 111 generated by the leading aircraft110 a. This information may be useful as a diagnostic tool (e.g., toverify the operational state of the tracer director 120), and/or toprovide information about the location of the vortex 111. The system 100can also include a second airborne detector 133 positioned to detect thevortices of another aircraft. For example, the second airborne detector133 on the following aircraft 110 b can be positioned to detect thevortex 111 generated by the leading aircraft 110 a.

The information generated by the tracer detector 130 can be provided toa communication network 140 for distribution to other components of theoverall system 100, as appropriate. Accordingly, the communicationnetwork 140 can include ground stations 141 that support air-to-groundlinks 142 with the aircraft 110 a, 110 b. The ground stations 141 canalso communicate with overhead satellites 104 which may provideadditional information. Still further information may be provided byweather sensors 103 and the ground-based detector 131. An informationmanagement system 101 controls and manages the information provided tothe communications network 140 via a processor 102 or other suitabledevice. In particular instances, the processor 102 may also housepredictive tools, such as those disclosed in co-pending U.S. applicationSer. No. 11/463,685 previously incorporated by reference. Predictionscarried out by these tools may be compared with actual data received bythe tracer detector 130.

The communications network 140 can route the information received fromthe tracer detector 130 to the appropriate locations. One such locationincludes an air traffic services (ATS) facility 150, at which airtraffic controllers view an air traffic display 151. A representation152 of the vortices detected by the tracer detector 130 can be overlaidon the air traffic display 151 to aid an air traffic controller 153 inrouting the aircraft within his or her control. In particular, the airtraffic controller 153 can use this information to direct the followingaircraft 110 b, which is potentially affected by the vortices 111generated by the leading aircraft 110 a. Information may also becommunicated directly to the following aircraft 110 b from the groundstations 141, or from the leading aircraft 110 a, via an air-to-air link143. Accordingly, the operator of the leading aircraft 110 a may haveinformation about the vortices generated by his or her aircraft, the airtraffic controller 153 can receive and act upon this information, andthe operator of the following aircraft 110 b can also receive and actupon this information, either directly, or with the assistance of theair traffic controller 153.

FIG. 2 is a partially schematic, isometric illustration of arepresentative aircraft 110 (e.g., a commercial passenger and/or cargotransport aircraft) carrying several tracer directors 120 (illustratedas tracer directors 120 a-120 e) configured in accordance with severalembodiments of the invention. In general, it is expected that a givenaircraft 110 will include only one such tracer director, but forpurposes of illustration, several different types of tracer directorsare shown on the same aircraft 110 in FIG. 2. In particular embodimentsdescribed further below, the aircraft 110 can include multiple tracerdirectors.

The aircraft 110 can include a fuselage 114, wings 160, and engines 116which provide the main propulsive force for the aircraft 110. In anembodiment shown in FIG. 2, the engines 116 are carried by the wings160, but in other embodiments, the engines 116 may be carried by thefuselage 114 or other portions of the aircraft 110. In a particularembodiment shown in FIG. 2, a first tracer director 120 a is housed inone or both of the wings 160. For purposes of illustration, the firsttracer director 120 a is shown housed in only one of the wings 160. Thefirst tracer director 120 a can be coupled to a reservoir 121 whichcarries tracer elements directed into the vortices 111 by the firsttracer director 120 a, and a controller 122, which manages the operationof the tracer director(s) 120. The tracer elements can include any of awide variety of elements that are detectable by the tracer detector 130(FIG. 1). In particular embodiments, the tracer elements are visuallydistinguishable to an unaided observer, and in other embodiments, thetracers are not visually distinguishable from their immediatesurroundings by an unaided observer, either on a following aircraft, oron the ground. For example, the tracer elements can include an energizedgas, such as ammonia, which is directed from the wing 160 into thevortex 111. Further detail of this and other embodiments of the tracersare described in greater detail below with reference to FIG. 5.

In other embodiments, the tracer director can be located at portions ofthe aircraft 110 other than the wing tip. For example, a representativesecond tracer director 120 b can be positioned proximate to a flap orother high lift device 164 of the aircraft 110. This location may besuitable when it is expected that the strongest and/or most easilydetected vortices generated by the aircraft are those generated byand/or proximate to the high lift devices 164. In still furtherembodiments, the tracer detectors can be positioned at other locationson the aircraft. For example, a third tracer director 120 c can becarried by the engine 116 so as to emit tracers via the engine exhauststream. This arrangement may be suitable where the engine exhaust streamis expected to be entrained by the aircraft vortices, for example,vortices generated by the flaps or other wing high lift devices 164.

The first, second, and third tracer directors 120 a-120 c describedabove can be coupled to the reservoir 121 which delivers physicalmaterial to the corresponding tracer director for ejection into theadjacent vortical flow. The material can include a gas, liquid, solid,vapor or mist. In other embodiments, the tracer director can directenergy, rather than physical particles, into the vortical flow. In suchcases, the tracer director can have any of the locations described abovewith reference to the tracer directors 120 a-120 c. Alternatively, thetracer director can direct energy into the vortical flow from a moreremote location. For example, fourth and fifth tracer directors 120 dand 120 e can be positioned in the tail and fuselage, respectively ofthe aircraft 110 and aimed laterally toward the vortices 111. In anotherembodiment described below with reference to FIG. 4, a general similartracer director can be positioned closer to the wing tip. It is expectedthat the energy directed into the vortices 111 by the tracer directors120 d, 120 e will be absorbed by molecules in the vortical flow. Theabsorbed energy can make the molecules more visible e.g., by ionizingthe molecules, or when the energy is re-emitted by the molecules (via achange in molecular energy state and/or electronic energy state). Ineither embodiment, the effect of the energy is to make the vortical flowdetectable or more detectable by the tracer detector 130 (FIG. 1).

In a particular embodiment, one or more of the tracer directors 120a-120 e may be carried by the same aircraft 110. For example, theaircraft 110 can include multiple independent or partially independenttracer directors for purposes of redundancy. In other embodiments, theaircraft 110 can include multiple tracer directors that are configuredto work together. For example, the aircraft 110 can include one tracerdirector (e.g., one of tracer directors 120 a-120 c) to direct aphysical substance into the vortical flow, and another (e.g., one of thetracer directors 120 d-120 e) to add energy to the physical substanceand/or the vortical flow generally.

FIG. 3 is an enlarged, partially schematic illustration of the wing 160shown in FIG. 2, along with the first and second tracer directors 120 a,120 b. The first tracer director 120 a can receive tracer elements fromthe reservoir 121 and direct them through any of a variety of deliveryapertures 163. For example, the tracer elements can be directed throughone or more delivery apertures 163 a located in a wing tip 161, one ormore delivery apertures 163 b located at the trailing edge of the wing160, and/or one or more delivery apertures 163 c located in a winglet162 of the wing 160. The second tracer director 120 b can direct tracerelements through one or more delivery apertures 163 d located at theinboard and/or outboard tips of the wing flap or other high lift device164. In another embodiment, delivery apertures 163 e can be positionedin the wing 160 along the opening into which the high lift device 164retracts. The number of delivery apertures 163 a-163 d shown in FIG. 3is representative of particular embodiments. In other embodiments, thenumber of delivery apertures 163 a-163 d can be smaller (e.g., a singledelivery aperture 163 a-163 d for each corresponding location) orgreater than the number shown in FIG. 3.

FIG. 4 is a partially schematic illustration of the wing 160 with asixth tracer director 120 f positioned at the wing tip 161 to directenergy into the adjacent vortical flow. In one embodiment, the sixthtracer director 120 f can include an ionizer that ionizes air moleculesproximate to the wing tip 161. The ionizer can include one or moreelectrically charged sharp or pointy surfaces that effectively ionizeadjacent air molecules. The ionized air molecules are expected to bemore highly reflective to radar (or other electromagnetic waves) thanare the surrounding non-ionized molecules. Accordingly, the ionizedmolecules can provide an indication of the vortex location.

FIG. 5 is a flow diagram illustrating a process 500 for directingtracers into a vortical flow using one or more of the tracer directorsdescribed above. Process portion 501 includes generating a vortical flowin air adjacent to an aircraft. Process portion 502 includes directing atracer from the aircraft into the vortical flow. The tracer can bedirected into the vortical flow in a constant manner, as indicated atblock 503, or in a time-varying manner, as indicated at block 504. Oneexpected advantage associated with directing the tracer in atime-varying manner is that doing so may make the tracer moredistinguishable from its environment. For example, if the surroundingenvironment provides a steady state background noise level picked up bythe tracer detector, then a tracer that appears in a time varying manneris likely to stand out more distinctly against the background. If thesurrounding environment provides a time-varying background noise levelpicked up by the tracer detector, then the tracer can be emitted in amanner that varies with time differently than does the background noise.Appropriate filtering techniques can then be used to segregate thedesired signal (associated with the tracer) from the background noise(associated with the environment).

In process portion 505, a physical substance is directed into thevortical flow. The physical substance can include a gas (block 506) agas-filled balloon or other type of envelope (block 507), chaff (block508), or other substances (block 509). When a gas is directed into thevortical flow, it can be selected in accordance with several designcriteria, including its compatibility with the environment and itsbuoyancy. For example, ammonia can be selected because it is lighterthan air and, due to the centrifugal force produced in the vortex, istherefore expected to be forced toward the core or center of the vortex.As a result, ammonia (or another buoyant gas) is expected to remain withthe vortex for a relatively long period of time, and therefore provide arelatively long-lived indication of the vortex's presence. Ammonia isalso expected to have a relatively low environmental impact on theregion over which is it dispersed.

Ammonia can be excited (e.g., via an ammonia maser or other microwavedevice) at a resonant frequency of 23.9 GHz, effectively producing amicrowave fluorescence. In other embodiments, other devices may be usedto excite the ammonia. In other embodiments, the ammonia can be excitedat other frequencies around the resonant frequency (e.g., to accommodateline broadening). Ammonia (NH₃) has a strong dipole moment and canreadily undergo a room temperature “nitrogen inversion,” in which thenitrogen atom passes through the plane formed by the three hydrogenatoms, at an energy of 24.7 kJoule/mole which corresponds to the 23.9GHz. resonant frequency. This resonant frequency in turn corresponds toa microwave radiation wavelength of 1.26 centimeters, which is close tothe original K-band radar of 24 GHz. This is near but on the high sideof the absorption band for water and therefore is expected to besufficiently detectable or distinguishable from water molecules. Ammoniaalso has infrared absorption/emission bands at wavelengths of 2.9, 3.0,6.146, and 10.53 microns. Accordingly, infrared techniques, rather thanradar techniques, may alternatively be used to detect ammonia.

In other embodiments, the tracer can include a gas other than ammonia.For example, other gases which have been examined, but are expected notto be desirable as ammonia include hydrogen, helium, methane, watervapor, hydrogen fluoride, neon, acetylene, diborane, carbon monoxide,nitrogen, and ethylene. In still further embodiments, other gases or gasmixtures may be used. For example, individual gases that are generallyundetectable when apart, but detectable when mixed, can be mixed anddischarged from the aircraft as tracers.

If a gas-filled balloon is used as a tracer element (block 507), the gasmay be selected to be buoyant, as described above, and the balloon maybe selected to be biodegradable. In a particular embodiment, the gas maybe selected not only to be buoyant, but also to chemically react withthe balloon so as to hasten its degradation. Accordingly, microballoonsmay be filled with such a gas immediately prior to being deployed fromthe aircraft. Once deployed, the buoyant gas within the balloon willtend to keep the balloon within the vortex core. The characteristics ofthe gas and the balloon can be selected using techniques known to thoseof ordinary skill in the relevant art to cause the balloon to dissolveafter a selected time period (e.g., about one minute), allowingsufficient time to detect the balloon, and then the balloon can degradecompletely or at least partially before reaching the ground. Forexample, the gas can include an acidic or other corrosive component.

If chaff is selected as the tracer element (block 508), it may beselected to be especially reflective at particular wavelengths, e.g.,radar wavelengths. The chaff may also to be readily biodegradable, inthe air and/or upon reaching the ground.

Other substances (block 509) may also be used as tracer elements. Forexample, very small carbon dioxide crystals can be directed into thevortical flow, where they can reflect radar energy. In anotherembodiment, the tracer elements can include crystals formed from localconstituents. For example, the crystals can be formed from ambient watervapor and/or water vapor present in the engine exhaust. These crystalscan form contrails or contrail-like structures that are detectablevisually or by other detectors. In still another embodiment, the tracerelements can be self-powered (e.g., with a battery) and can emit radiosignals, or the elements can receive radio signals (or signals at otherwavelengths) and reemit radiation which is then detected. Accordingly,these elements can operate in the manner of self-powered or stimulatedRFID devices. These elements may be selected to be buoyant compared toair molecules, and readily biodegradable. Buoyancy can be increased byadding a lighter-than-air gas to the tracer, or by adding a parachute orsimilar device. Micro- or nano-particles can be formed into 3-D shapes,with a bonding agent that allows the particles to decompose rapidly inthe presence of water vapor or sunlight. Suitable water-soluble agentsand UV-sensitive agents are well known to those of ordinary skill in therelevant art.

Optionally, energy can be added to the tracer for increaseddetectability (block 510). For example, if the tracer in its normalstate is not highly detectable, energy can be added to the tracer priorto release from the aircraft (block 511). Energy can be added to thetracer after release (block 512), either in addition to or in lieu ofadding energy prior to release. For example, if the tracer emits energyover such a short time period that it is not easily detected, thenenergy can be added to the tracer after it has been released. If in someinstances it is easier to add energy to the tracer after it has beenreleased than before it has been released, a similar process can beused. In a particular embodiment, ammonia may be excited by a maserprior to release. If, after release, the ammonia emits energy tooquickly to be readily detected by an aircraft or ground-based detector,then energy may be added to the ammonia in a post-release process toincrease the chances for detecting this tracer element. Energy may beadded to the tracers either from an airborne energy source (block 513),e.g., an energy source carried by the same aircraft as carries thetracer, or from a ground-based energy source (block 514), or both.

As discussed initially with reference to FIG. 2, an alternative approachto directing a physical substance into the vortical flow (processportion 505) includes directing energy into the flow without introducinga separate physical substance (process portion 515). For example, theair adjacent to the wing tip can be ionized by an air ionizer positionedat the wing tip (block 516). The charged ions produced by this processare expected to reflect energy, for example, radar energy, moreeffectively than nearby non-ionized molecules. Accordingly, a radardetector can be used to identify the ionized molecules. A tungstenelectron emitter can be used for ionization, and any of the constituentsof air can be ionized depending upon the energy provided. Other ionizerscan include vacuum ultraviolet light ionizers, extreme ultraviolet lightionizers, and/or an X-ray emitter. Typical ionization techniques includethermionic emission, field emission, secondary electron emission, thephotoelectric effect, cathode rays, charged particle radioactivity, andhigh-energy electromagnetic radiation. Any of these techniques may beused alone or in combination to generate the desired ions.

Alternatively, the electronic energy state of the molecule may beincreased (block 517). Rather than charging the molecules in anionization process, block 517 includes moving electrons of the moleculefrom a low or relatively low electronic energy state to a higherelectronic energy state. As the electrons descend back to the low energystate, they emit radiation which is then detected by a ground- orair-based detector. In still other embodiments, other techniques fordirecting energy into the flow may be used (block 518).

FIG. 6 illustrates a process 600 for detecting the presence of thetracers described above with reference to FIG. 5. Process portion 601includes detecting a characteristic associated with the presence of atracer directed from an aircraft into vortical flow. As discussed above,the tracer can include a physical substance directed from the aircraft,energy directed from the aircraft (e.g., energy which is absorbed andre-emitted by the adjacent air), or a combination of a physicalsubstance and energy. Detection techniques include radar (e.g., K-bandfor ammonia, or X-band for ionized air, or Ka band or W band for othersubstances) lidar, infrared, acoustic, optical or others. Process 600can include detecting the characteristic from the ground (block 602)and/or from another aircraft (block 603). Optionally, the detectionsignal associated with detecting the characteristic can be analyzed(block 604). For example, if the tracers are ejected from the aircraftor otherwise created in a constant process, the signal can be analyzedin accordance with one technique (block 605). If the tracers are ejectedor generated in a time varying manner, the signal can be analyzed inaccordance with another technique (block 606).

In process portion 607, a response signal is generated, based at leastin part upon the detection of the tracer identified in block 601. Theresponse signal can be directed to another aircraft (block 608), or tothe ground (block 610). If the response signal is directed to anotheraircraft, it can also (optionally) be directed to the ground (block609). If the response signal is directed to the ground, it can also(optionally) be directed to another aircraft (block 611). The responsesignal can be made evident to a pilot and/or controller by visual, auraland/or other annunciation techniques.

Process portion 612 includes directing aircraft routing, based at leastin part upon the response signal. For example, a following aircraft canbe directed to evade a vortex (process portion 613). Alternatively (oradditionally), the following distance for the following aircraft can bedetermined, based at least in part on the detection of the vortex(process portion 614). Alternatively (or additionally), the path of theleading aircraft (e.g., the aircraft associated with the detectedvortex) can be changed (process portion 615).

FIG. 7 is a partially schematic and compressed illustration of anaircraft 110 approaching a ground-based detector 131 located near anactive runway 770. The detector 131 can be aligned with anapproach/departure axis 771 of the runway 770. For purposes ofillustration, the detector 131 is shown at the end of the runway 770,but it can also be located at other points along the axis 771. Thedetector 131 can be configured in accordance with any of the foregoingembodiments above, and can accordingly include a radar detector, lidardetector, infrared detector, acoustic detector, optical detector, orother suitable instrument configured to detect a characteristicassociated with the tracer emitted by the aircraft 110. Unlike existingdetectors, the detector 131 shown in FIG. 7 can have a detection axis734 that is aligned with the approach/departure axis 771. This is so forat least the reason that the detector 131 need not direct energytransverse to the vortices 111 (as is the case with Doppler-baseddetectors), but can instead detect the characteristics of the tracer inthe vortices 111 from any angle. An expected advantage of thisarrangement is that the number of detectors required to generate theinformation used to route aircraft can be significantly reduced whencompared with existing arrangements. A further expected advantage ofthis arrangement is that the detector 131 can more easily detectvortices generated by aircraft that are off-axis relative to thedetector 131, without the need for a large network of detectors.

Furthermore, a ground-based radar (e.g., K-band radar) can be steered inazimuth and elevation to provide two dimensions of reference for thedetected vortex. When used to receive energy pulses, range-gating can beused to provide a third or depth dimension. This arrangement can allowfor three-dimensional visualization of the wake vortices.

In still further embodiments, the ground-based detector 131 can haveother arrangements. For example, the detector 131 can include a networkof distributed, spaced-apart detector elements that have known locationsrelative to each other. Each of these detector elements can detect acharacteristic of the tracer. Using phase-shift information and theknown distances between detector elements, the system can establish atomographic map or other representation of the vortex locations. In aparticular embodiment, the detector elements can be relatively low-costdevices, located on existing platforms (e.g., cell phone towers) and canbe networked using existing network facilities (e.g., a cell phonenetwork).

One feature of at least some embodiments of the foregoing systems andmethods is that they include actually detecting characteristicsassociated with vortices or other vortical flow for aircraft on anindividual basis. An expected advantage of this feature is that in manyinstances, the actual vortex characteristics are likely to be morebenign than the “worst-case” characteristics that are conventionallyassumed when determining aircraft routes and following distances.Accordingly, it is expected that aircraft following distances may bedecreased because the determination of the following distances may bebased on case-by-case, actual information, rather than an assumed worstcase scenario. In other instances, the following aircraft may bedirected to make minor course adjustments to avoid the vortex, withoutthe need for a large following distance. As a result, in at least somecases, it is expected that embodiments of the foregoing systems andmethods can increase airport capacity in the range of 50-100%.

Another feature of at least some of the foregoing embodiments is thatthe equipment for emitting a tracer and, optionally, the equipment fordetecting the tracer, can be carried by one or more aircraft. Anadvantage of this arrangement is that vortices can be detected inregions that are remote from airports, which is where such equipment isconventionally located. As a result, aircraft flying in remote areas canreceive vortex information from aircraft up ahead, and can takeappropriate action. Again, the information on which the action is basedis expected to be more accurate than the assumption of a worst casescenario, and accordingly, it is expected that following distances canbe reduced.

Still another feature of at least some of the foregoing embodiments isthat the tracer is not visually detectable by an unaided human observeron the ground (e.g., with the naked eye), or to an unaided pilot in afollowing aircraft. Accordingly, these tracers are unlike visible smoketrails emitted by stunt aircraft, or smoke tracers used for flowvisualization during research or experimental flights. An advantage ofthis feature is that in both crowded air terminal control areas and inlocations remote from airports, the tracer is not expected to contributeto visual pollution, which can be an environmental issue and can createconfusion to aircraft pilots.

From the foregoing, it will be appreciated that specific embodimentshave been described herein for purposes of illustration, but thatvarious modifications may be made without deviating from the invention.For example, non-buoyant materials can be used where it is determinedthat viscous entertainment will keep the tracer in the vortex for asufficient period of time. Certain aspects of the invention described inthe context of particular embodiments may be combined or eliminated inother embodiments. For example, the overall system shown in FIG. 1 caninclude more or fewer components and/or component combinations. Further,while advantages associated with certain embodiments of the inventionhave been described in the context of those embodiments, otherembodiments may also exhibit such advantages, and not all embodimentsneed necessarily exhibit such advantages to fall within the scope of theinvention. Accordingly, the invention is not limited except as by theappended claims.

1. A method for identifying aircraft vortical flows, comprising:directing a tracer from a first aircraft into a vortical flow generatedby the first aircraft; detecting a characteristic corresponding to thepresence of the tracer directed into the vortical flow; and based atleast in part on the detected characteristic, directing the flight ofthe first aircraft, or a second aircraft following the first aircraft,or both.
 2. The method of claim 1, further comprising: generating asignal in response to detecting the characteristic; transmitting thesignal to at least one of an air traffic control and the secondaircraft; and based at least in part on the generated signal: (a)controlling a separation distance between the first aircraft and thesecond aircraft; (b) directing the second aircraft away from thevortical flow; or (c) both (a) and (b).
 3. The method of claim 1 whereindirecting a tracer includes directing a tracer that is visuallyindistinguishable from the ground and the second aircraft.
 4. The methodof claim 1 wherein directing a tracer includes directing the tracer in atime-varying manner.
 5. The method of claim 1 wherein directing a tracerincludes directing a gas into the vortical flow.
 6. The method of claim5 wherein directing a gas includes directing a gas that is lighter thanair.
 7. The method of claim 1 wherein directing a tracer includesdirecting energy into the vortical flow and changing a characteristic ofa molecule in the vortical flow with the energy.
 8. The method of claim1 wherein directing a tracer includes directing a tracer having anenvelope at least partially filled with a gas.
 9. The method of claim 1wherein directing a tracer includes directing chaff.
 10. The method ofclaim 1, further comprising increasing an energy of the tracer afterdirecting the tracer into the vortical flow.
 11. The method of claim 10wherein increasing an energy of the tracer includes increasing an energyof the tracer from a location on the ground.
 12. The method of claim 10wherein increasing an energy of the tracer includes increasing an energyof the tracer from a location onboard the first aircraft.
 13. The methodof claim 1 wherein detecting a characteristic corresponding to thepresence of the tracer includes detecting the characteristic from thesecond aircraft.
 14. The method of claim 1 wherein detecting acharacteristic corresponding to the presence of the tracer includesdetecting the characteristic from the ground.
 15. The method of claim 1wherein detecting a characteristic corresponding to the presence of thetracer includes using radar to detect an ionized gas.
 16. A method foridentifying aircraft vortical flows, comprising: generating a vorticalflow in air adjacent to an aircraft by moving the aircraft relative tothe adjacent air; and directing a tracer from the aircraft into thevortical flow, the tracer being visually indistinguishable from itssurroundings to an unaided observer on the ground or in a followingaircraft while the tracer is in the vortical flow.
 17. The method ofclaim 16 wherein the aircraft is a first aircraft, and wherein themethod further comprises: detecting a characteristic corresponding tothe presence of the tracer directed into the vortical flow; generating asignal in response to detecting the characteristic; transmitting thesignal to at least one of an air traffic control system and a secondaircraft following the first aircraft; and based at least in part on thegenerated signal: (a) controlling a separation distance between thefirst aircraft and a second aircraft following the first aircraft; (b)directing the second aircraft away from the vortical flow; or (c) both(a) and (b).
 18. The method of claim 16 wherein directing a tracerincludes directing a tracer during a commercial flight while carrying arevenue-generating payload.
 19. The method of claim 16 wherein directinga tracer includes directing the tracer in a time-varying manner.
 20. Themethod of claim 16 wherein directing a tracer includes directing a gasinto the vortical flow.
 21. The method of claim 20 wherein directing agas includes directing a gas that is lighter than air.
 22. The method ofclaim 20 wherein directing a gas includes directing ammonia.
 23. Themethod of claim 16 wherein directing a tracer includes directing energyinto the vortical flow and changing a characteristic of a molecule inthe vortical flow with the energy.
 24. The method of claim 23 whereinchanging a characteristic includes ionizing air molecules in thevortical flow.
 25. The method of claim 16 wherein directing a tracerincludes directing a tracer that decomposes more rapidly after beingdirected into the flow than before being directed into the flow.
 26. Themethod of claim 16 wherein directing a tracer includes directing atracer having an envelope at least partially filled with a gas.
 27. Themethod of claim 26, further comprising filling the envelope with a gasthat decomposes the envelope.
 28. The method of claim 16 whereindirecting a tracer includes directing chaff.
 29. The method of claim 16,further comprising increasing an energy state of electrons of the tracerwhile the tracer is aboard the aircraft and before directing the tracerinto the vortical flow.
 30. The method of claim 16, further comprisingchanging a molecular energy state of the tracer while the tracer isaboard the aircraft and before directing the tracer into the vorticalflow.
 31. The method of claim 16, further comprising increasing anenergy of the tracer after directing the tracer into the vortical flow.32. The method of claim 31 wherein increasing an energy of the tracerincludes increasing an energy of the tracer from a location on theground.
 33. The method of claim 31 wherein increasing an energy of thetracer includes increasing an energy of the tracer from a locationonboard the aircraft.
 34. A method for identifying aircraft vorticalflows, comprising: detecting a characteristic corresponding to thepresence of a tracer directed from an aircraft into vortical flow in airadjacent to the aircraft as the aircraft moves relative to the adjacentair, the tracer being visually indistinguishable from its surroundingsto an unaided observer on the ground or in a following aircraft whilethe tracer is in the vortical flow; and generating a signal in responseto detecting the presence of the tracer.
 35. The method of claim 34wherein the aircraft is a first aircraft, and wherein the method furthercomprises: based at least in part on the generated signal: (a)controlling a separation distance between the first aircraft and asecond aircraft following the first aircraft; (b) directing the secondaircraft away from the vortical flow; or (c) both (a) and (b).
 36. Themethod of claim 34 wherein detecting a characteristic corresponding tothe presence of the tracer includes detecting the characteristic fromanother aircraft.
 37. The method of claim 34 wherein detecting acharacteristic corresponding to the presence of the tracer includesdetecting the characteristic from the ground.
 38. The method of claim34, further comprising increasing an energy of the tracer after thetracer has been directed from the aircraft, from a location that isremote from the aircraft.
 39. The method of claim 34, further comprisingadding energy to the tracer and detecting energy emitted by the tracer.40. The method of claim 34, further comprising directing anotheraircraft away from the vortical flow in response to detecting thepresence of the tracer.
 41. The method of claim 34 wherein detecting thecharacteristic corresponding to the presence of the tracer includesdetecting energy emitted by the tracer.
 42. The method of claim 34wherein the tracer is directed from the aircraft in a time varyingmanner, and wherein detecting a characteristic corresponding to thepresence of the tracer includes distinguishing the time varying mannerof the directed tracer from characteristics of the environmentsurrounding the tracer.
 43. An aircraft, comprising: a payload volume; alifting surface positioned to generate lift and an associated vorticalflow; and an on-board vortical flow tracer system that includes: atracer director positioned to direct a tracer into vortical flowgenerated by the lifting surface, the tracer being visuallyindistinguishable from its surroundings to an unaided observer on theground or in a following aircraft while the tracer is in the vorticalflow; and a controller operatively coupled to the tracer director toselectively activate the tracer director.
 44. The system of claim 43wherein the lifting surface includes a wing having a wing tip, andwherein the tracer director is positioned at least proximate to the wingtip.
 45. The system of claim 43, further comprising a tracer reservoircoupled to the tracer director.
 46. The system of claim 45 furthercomprising the tracer, carried by the tracer reservoir.
 47. The systemof claim 43 wherein the tracer director includes an energy emitter, andwherein the tracer includes energy.
 48. The method of claim 47 whereinthe energy emitter includes an ionizer.
 49. The system of claim 43wherein the tracer system includes an energy source positioned at leastproximate to the tracer director, the energy source being operativelycoupled to the controller to add energy to the tracer.
 50. The system ofclaim 49 wherein the energy source is positioned to direct energy to thetracer after the tracer has been directed from the aircraft.
 51. Thesystem of claim 49 wherein the energy source is positioned to directenergy to the tracer before the tracer has been directed from theaircraft.
 52. The system of claim 49 wherein the energy source includesan ammonia maser and wherein the tracer includes ammonia.
 53. A systemfor identifying vortical flow, comprising: a ground-based vortical flowtracer detector having a detection vector aligned at least approximatelyaxially with an active runway final approach/departure axis; acontroller operatively coupled to the detector; and an output deviceoperatively coupled to the detector to provide an indication when thedetector identifies tracers in a vortical flow.
 54. The system of claim53 wherein the detector includes at least one of a radio signaldetector, radar detector, lidar detector, and optical detector.
 55. Thesystem of claim 53 wherein the output device is located at an airtraffic control station.
 56. The system of claim 53 wherein the outputdevice is located on board an aircraft.